The present invention relates to sheets for lining denture base.
The "lining denture base" is the abbreviated expression indicating the material which lines one of the surfaces of a dental base, particularly the surface which faces to the gingival- and palatal surface in the mouth.
Hitherto, resins derived from methacrylates have been used for manufacturing denture base. However, in the cases where the absorption by the alveolar arch is strong, there cases where desirable results can not be obtained by the denture base solely made of methacrylate resin. In such cases, there are possibilities of causing pain on the thin gingival mucosa got between the hard denture base and the gingiva, the pain occasionally leading to a kind of ulcer. Consequently it is necessary to line the denture base facing to the gingival mucosa which has come to be thinner by the use of the hard denture base with a material which is able to substitute the lost thickness of the original mucosa which is naturally elastic to a certain extent. The material for lining the surface of the denture base, which faces to the gingival membrane, playing a role of soft cushion is referred to as "soft lining denture base". The major role of the soft lining denture base is to compensate the lost thickness of the mucosa and to relax the impact of mastication as well as to disperse uniformly the masticatory pressure onto the mucosa.
In early days, as the soft material for lining denture base of methacrylate resin, vinyl polymers, copolymer of acrylate esters or one of those added with plasticizers has been applied. However, such a material could not give clinically satisfactory results for a long term because of its substantial instability such as swelling within the mouth due to absorption of moisture, deterioration due to aging and exuding foreign substances. Although a soft lining material for denture bases excellent in elasticity and water-proofness has been developed from derivatives of silicone thereafter, there are still problems to be solved such as insufficiency of adhesion to the resin constituting the denture base, liberation of the generation of bacteria such as Candida and difficulty of polishing the lined surface, etc.
Although methacrylate resin is still in use as the material for the denture base at present, it is preferable that the lining material for the denture base fulfills the following essential conditions:
(1) It is biologically safe for a long term.
(2) It does not deteriorate for a long period within the mouth and does not show any change in its pliability and mechanical properties.
(3) It adheres firmly to the methacrylate resin constituting the denture base without defoliating for a long period within the mouth.
(4) It is free from abrasion within the mouth.
(5) It is easily processable in cutting and polishing to have the smoothly polished surface and
(6) It is easily and conveniently processed by forming and finishing.
Attempts of substituting a fluoropolymer for polymethyl methacrylate of the dental base have been carried out, for instance, in U.S. Pat. No. 3,889,374, however, nothing is disclosed therein concerning the overcoming of the defects of polymethyl methacrylate as the material for lining denture base.
After studying with an intention of providing a material as the lining denture base provided with the specific characteristics, the present inventors have found that sheets prepared from a specified fluorine-containing copolymer are capable of fulfilling the demand for the specific characteristics, and have attained to the present invention.